Sorry, I made a slight mistake in my original post. I meant that
the GH10A/B/C require catalytic converters to meet
Euro 2/3/4. Diesel engines also require catalytic converters for
Euro 1 or stricter requirements.
Regarding CNG engines, here's a brief description on how they
work.
1. Natural gas fuel is stored at high pressure (up to 200 bar) in
cylinders usually mounted on the roof of a bus.
2. Gas is delivered to the engine bay from the cylinders via a high
pressure gas line.
3. Prior to entering the intake stream, the gas is filtered for
impurities and then depressurized to a set working pressure,
typically anywhere from zero pressure to 10 bar. This is done in
one or more pressure regulators, heated with coolant from the
radiator. The pressure regulator(s) may have one or more
stages.
4. The gas is then mixed with incoming air. This can be done at a
gas mixer (elementry carburettor) or via gas injectors.
5. Airflow is controlled by a butterfly valve in the intake stream
and in case of a turbocharged engine, a wastegate in the exhauast
stream.
6. When the air/fuel mixture reaches the engine, it is ignited by
spark plugs that are connected to the engine's ignition control
system.
Regards,
Dave
